Rare%20D%20EPS2005%20Lisbon

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The Rare and forbidden decays D ? hee- and
h-ee
David H. Miller Purdue University (Representing
the CLEO collaboration) HEP2005, Lisbon,
Portugal July 21st 27th , 2005
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Search for D ? hee-, h-ee
PRD 64, 114009 (2001)

• The search for rare decays has the potential to
  provide the observation of physics beyond the
  standard model. In the case of D ? hee- ,
  which is a FCNC decay, the expected branching
  ratios are of the order of 10-7 except for
  p?(ee-).
• The decays D ? h-ee are forbidden.

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CLEO-c detector
B1 Tesla Track 93 of 4p RICH 80 of 4p CsI
93 of 4p 0.6 P 1GeV/c 2.2 E? 1 GeV 5 E?
100 MeV
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Production at the ?(3770)
The ?(3770) is just above threshold for DD
production and each D is produced having energy
equal to the beam energy with equal and opposite
momenta. Therefore to select an exclusive decay
requires a set of particles satisfying energy and
momentum conservation. Particle ID is essential
for the selection of rare decays and rejecting
the copious hadronic decays. Electron E/P,
dE/dx , RICH P gt 200MeV/c K, p
dE/dx , RICH P gt 50 MeV/c
bremsstrahlung photons are added along the
direction of the electron
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Data set and event selection

• Data set is 281pb-1 at the ?(3770) taken with
  CLEO-c
• For many analyses we use a fully reconstructed D
  as a tag and then analyse the other D decay.
• In this analysis we use an un tagged analysis to
  improve sensitivity
• We use two kinematic variables to select our
  candidates
• ?E ED Ebeam
  
• (signal box is 20MeV)
  (resolution is 6 MeV)
• ?Mbc v(E2beam p2D) MD
  
• (signal box is 5 MeV/c2) (resolution
  is 1.5 MeV/c2)
• Multiple candidates are resolved by taking
  the best ?Mbc

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?Mbc and ?E
If particle ID is not used there is a large
hadronic background in this channel from
K-pp The signal box is defined by 5 MeV/c2
for ?Mbc 20MeV for ?E
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q2 selection for p?(ee-)
Because of the enhanced decay rate expected for
the decay p?(ee-) we divide the analysis into
two q2 regions for p?(ee-) 0.9973 lt q2 lt
1.0813 for pee- all other q2
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Background Rejection
MC ? conversion ?0 Dalitz decay
Data

• ? conversion and Dalitz decays are suppressed by
  a low q2 cut
• Double semileptonic decays rejected by event
  missing energy
• K0s e?e is suppressed using a K0s to pp veto
• cuts were optimized using Monte Carlo to give the
  best sensitivity

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Suppression cuts
Channel q2(GeV/c2)2 q2other(GeV/c2)2 Eother(GeV) ?MK0s(MeV/c2)
?ee- 0.01lt 0.0025lt 1.0lt -5,5)
?-ee 0.0025lt 0.500ltif Ntrack?4
Kee- 0.01lt 0.0025lt 1.3lt
K-ee 0.0025lt 0.500ltif Ntrack?4
??(ee-) 0.01lt 0.0025lt -5,5)

• q2ee suppress ?-conversion and
  ?0/?-Dalitz decays
• q2other is for an electron and any other
  oppositely charged particle
• Eother-side ( event missing energy) to veto
  double semileptonic
• ?MK0s to suppress D?K0seve

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Acceptance
A phase space model is used to determine signal
efficiencies and the efficiencies are uniform
except at the lower corners due to the electron
identification cutoff of 200MeV/c
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Final selection
The plots show the ?E distribution with ?Mbc 5
MeV/c2
no electron ID
One electron ID
Both electron ID and background suppression
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Open the signal box
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Final results
Channel e Nexpected Nobserved UL _at_90 CL
?ee- 36.41 1.99 2.0 7.4 x 10-6
?-ee 43.85 0.48 0.0 3.6 x 10-6
Kee- 26.18 1.47 0.0 6.2 x 10-6
K-ee 35.44 0.50 0.0 4.5 x 10-6
??(ee-) 46.22 0.04 2.0 B(2.8?1.9 ?0.2) x 10-6